-LRB- CNN -RRB- -- Travel warnings from the U.S. Department of State did n't stop Faith Hentschel , 65 , from venturing to Iran this May to visit the rustic sites in ancient Persepolis and the colorful bazaars in Tehran .

A photo of Khaju Bridge in Isfahan , Iran , taken by an American traveler .

`` I had no idea what to expect , '' said Hentschel , who spent two weeks in Iran after booking the trip through a private tour operator and applying for a visa . `` I was stunned with the friendliness of all the Iranian people . That alone makes me want to go back . ''

Iran is still a relatively rare destination for Americans , creating a niche market for only a handful of tour operators across the nation that organize group trips for travelers once or twice a year . And with news of the arrest of three American backpackers , along with the June election riots and government crackdown , Iran may be an even harder sell , some travel companies said .

`` It really depends on the political climate and the perception of Iran , '' said Mike McDonnell , who operates the site BestIranTravel.com in San Francisco , California . The site books trips for non-Iranian travelers interested in visiting . His site saw a decline in booking travel to Iran this summer . `` It 's already really hard to get to Iran in the first place . ''

Officials at the U.S. Department of State say travel warnings have been implemented on Iran since the hostage crisis in 1979 , when militants captured 52 American diplomats and staff . The Americans were held for 444 days . Since then , the two countries have had no diplomatic relations .

U.S. passports are valid for travel to Iran and visas are required to enter the country , according to the State Department Web site . Going with an organized tour group is the easiest way to attain a visa . Travelers who do visit Iran run the risk of being denied entry , U.S. officials say . In some cases , Iranian officials have prevented American citizens , academics , scientists and journalists from leaving the country , and even detained , interrogated and imprisoned some on unknown or various charges , the Web site said .

`` It 's made well-known that the destination -LSB- Iran -RSB- could be perilous for American citizens , '' said Darby Holladay , spokesman at the State Department .

Last week , three Americans were detained after crossing into northern Iran during a hiking trip . The two men and one woman , said to be seasoned travelers , began their trip in Turkey and went into Iraq before crossing the unmarked border into Iran . The U.S. State Department and the Australian and British government warn against traveling into the border zones .

`` Obviously , we are concerned , '' Secretary of State Hillary Clinton said Monday to reporters . `` We want this matter brought to a resolution as soon as possible . ''

Mudhafer Mohammed , owner of the Miwan Hotel , told CNN that the hikers said they had come to the area because they heard it was safe . Mohammed said he tried to discourage them from going to Ahmed Awa , a popular tourist destination in the northern Kurdish region of Iraq .

`` I told them , ` Do n't go there because it is unsafe for you because you 're American and Ahmed Awa is very close to the Iranian border , ' '' Mohammed told CNN . It is unclear whether the three wandered into Iran accidentally or intentionally entered the country .

Pauline Frommer , creator of the Pauline Frommer 's Travel Guides , said it 's safer when visiting countries in conflict to use travel companies and tour operators that rely on local accommodations and guides . She warned against staying in big hotel chains , which have been targets in recent terrorist attacks in Indonesia and India .

`` When it 's an iffy destination , it 's always a good idea to try and travel under the radar , '' she said . `` You do n't want to be a target . ''

Despite worries about safety , demand for visiting Iran has grown in recent years . Last May , travel writer Rick Steves shot a 10-day video of his visit to Iran in a one-hour special that launched on PBS . The project cleared up misconceptions about Iran and sparked Americans ' interest in traveling there , travel experts said .

At Geographic Expeditions , a luxury travel company that organizes trips to Iran , the number of participants doubled from 25 in 2007 to 50 in 2008 . Spiekermann Travel Service , Inc. , one of the oldest travel agencies that specializes in Iranian travel , has booked more than 350 tours to the country since it began operating there in 1995 .

`` My path is known , '' said Ihab Zaki , owner of Spiekermann , which is based in Michigan . He said he began offering tours after he visited the country himself and was awed by its history and art .

`` We send all our paperwork to local governments and they know we are coming . I do n't let my people roam around in the middle of nowhere . It 's very safe . ''

But the recent uncertainty in Iran has caused interest to wane . Spiekermann 's bi-annual trips to Iran , limited to 14 travelers , usually sell out . But only four have signed up for the fall trip . Far Horizons Archaeological & Cultural Trips , Inc. in San Anselmo , California planned a second trip to Iran for October after their first trip in May sold out . But owner Mary Dell Lucas said the trip maybe be canceled because travelers are withdrawing .

`` What 's happening most recently is scaring people , '' she said . `` Those three Americans made a mistake , but with us , it 's very different . We are taking a group , and we are invited . ''

Lucas ' firm and other tour companies say they take precautions . Participants are required to abide by Iranian law , which means women must dress conservatively and cover their heads with scarves . A professor and a local guide , who are familiar with the country , accompany the American travelers .

Barbara Bailey , a 73-year-old from rural Ohio , went on a two-week vacation to Iran last April with a tour group . Her favorite part of the trip was talking to the Iranian women at the local restaurants .

`` I went because nobody has really been before , and I know they have a wonderful history , '' Bailey said . `` If you can get past the government , the people there are great . ''

If travelers ca n't afford to spend between $ 6,000 and $ 10,000 on organized excursions of two or three weeks and decide to backpack , they still need to follow the rules , said Jon Dorn , editor in chief of Backpackers Magazine .

`` If you 're going to a place that 's not like America , then do your homework on what 's appropriate , '' said Dorn . Backpackers Magazine , an online and print publication specializing in backpacking , hiking and travel , reaches 2.5 million readers in the U.S.

Dave Stevenson , who oversees the Web site www.travel-security-and-safety.com , said hikers should be equipped with GPS systems , satellite or cell phones and maps when traveling in border areas , especially in conflict zones . They should also notify relatives back home where they are hiking abroad .

`` The world is a big place , '' Stevenson said , `` And there are always plenty of places to hike that are n't dangerous or war zones . ''

CNN 's Arwa Damon contributed to this report .

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Three American hikers were detained last week by Iranian officials

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A handful of tour operators provide tours for Americans to visit Iran

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A U.S. passport is valid in Iran ; visitors need a visa

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Travel warnings for Iran have been in place since the 1979 hostage crisis